1. Field of the Invention
The present invention relates to focal-plane shutters.
2. Description of the Related Art
Conventionally, referring to Japanese Patent No. 3224786, there has been known a focal-plane shutter as employed in a single-lens reflex camera. FIGS. 1 and 2 illustrate such a conventional focal-plane shutter. FIG. 1 is a front view of the conventional focal-plane shutter, and FIG. 2 is a sectional view showing an essential part of the conventional focal-plane shutter. The conventional focal-plane shutter includes a shutter base plate 10x, a supporting plate 20x, a partition plate 30x, a thin plate 40x, a leading shutter 50x, a following shutter 60x, and a driving mechanism 70x. A printed circuit board 91x is located at the back side of the focal-plane shutter. An image pickup device 90x is mounted on the printed circuit board 91x. 
The shutter base plate 10x is located at an object side. The supporting plate 20x is located at an image side. A blade chamber which accommodates the leading shutter 50x and the following shutter 60x is defined by the shutter base plate 10x and the supporting plate 20x. The partition plate 30x is located between the leading shutter 50x and the following shutter 60x. The thin plate 40x is provided between the shutter base plate 10x and the leading shutter 50x. The thin plate 40x prevents the fluttering of distal end of the leading shutter 50x or the following shutter 60x when the leading shutter 50x or the following shutter 60x travels.
The leading shutter 50x is connected to arm members 81x and 82x, and actuation of the arm members 81x and 82x opens and closes an opening 11x. Likewise, the following shutter 60x is connected to arm members 83x and 84x, and actuation of the arm members 83x and 84x opens and closes the opening 11x. The driving mechanism 70x drives the arm members 81x to 84x. 
A mirror box M is disposed at the object side of the shutter base plate 10x, and represented by alternate long and short dashed lines in FIG. 2. As shown in FIG. 2, a sloping surface 12x is formed at an edge of the opening 11x and inclined upward from the shutter chamber to the object side.
Incidentally, the focal-plane shutter is also employed in a recent digital camera. As a high pixel density of the digital camera, even if a little dust attaches to the image pickup device, image quality may be adversely affected.
Therefore, periodical maintenance is required for this camera. For example, brush for sweeping or the like is inserted into the opening of the shutter base plate from the object side, and removing the dust attached to the image pickup device is needed.
However, in the conventional focal-plane shutter, as shown in FIG. 2, the shape of the edge of the opening 11x at the object side is not supposed for the insertion of such the cleaning tool. Additionally, in the cases where the shutter base plate or proximity of the opening is made of resin, it is difficult to manufacture the proximity of the opening to be thin. This does not allow the proximity of the opening to be thin, thus reducing a space for insertion of the cleaning tool and making the insertion of the cleaning tool difficult.
Hence, periodical maintenance is required for maintaining the image quality. Thus, it is preferable that the maintenance operation should be performed with ease.